Sometimes symptoms of stroke develop gradually. But if you are having a stroke, you are more likely to have one or more sudden warning signs like these: Numbness or weakness in your face, arm, or leg, especially on one side Confusion or trouble understanding other people Trouble speaking Trouble seeing with one or both eyes Trouble walking or staying balanced or coordinated Dizziness Severe headache that comes on for no known reason. How ever the first thing person should do with any similar symptoms is check your blood pressure and if its on higher side then take anti hypertensive pill and rush to hospital near by for immediate medical support. With your case it may be related with stroke but it always comes with combine symptoms of any above signs. But here she had only one symptom of loss of vision one side of eye. In that case it may be some thing else also. How ever I advice let her go for MRI brain and the report will conform the stroke if it was there. Or else let her visit a eye specialist if stroke is not conform in MRI report. I am sure this will be helpful if you follow it as per i suggested.